Various techniques are used for recognizing subscribers of telephone networks, for various purposes, such as authorized eavesdropping and location tracking of mobile subscribers. The subscribers are usually recognized according to their telephone identifiers in the network. Common identifiers in cellular networks are International Mobile Subscriber Identity (IMSI), Mobile Subscriber Integrated Services Digital Network Number (MSISDN) and International Mobile Equipment Identity (IMEI).
Text-independent speaker identification techniques are described, for example, by Reynolds and Rose, in “Robust Text-Independent Speaker Identification using Gaussian Mixture Speaker Models,” IEEE Transactions on Speech and Audio Processing, volume 3, no. 1, January, 1995, and by Monte et al., in “Text Independent Speaker Identification on Noisy Environments by Means of Self Organizing Maps,” Proceedings of the Fourth International Conference on Spoken Language (ICSLP), October, 1996, which are incorporated herein by reference.